1. Field of the Invention
The present invention relates to power supply generators of the type employed to drive ultrasonic transducers that are used in wire and die bonders. More particularly, the present invention relates to a system and a circuit for automatically tuning an ultrasonic generator to the resonant frequency of a particular ultrasonic transducer which contains a bonding tool and changes its resonant frequency under load.
2. Description of the Prior Art
Heretofore, manufacturers of ultrasonic power supply equipment have employed phase lock loop circuits (PLL) to enable ultrasonic power supply generators to track the resonant frequency of a transducer. Presumably, the phase lock loop circuit has a frequency range which accommodates the variations in resonant frequency which occur when the transducer is loaded under various conditions or different transducers and bonding tools are interchanged with the power supply which is an integral part of a bonder.
In prior art power supply generator systems, it was necessary to employ manual sweeping of the frequency of the transducer to find a resonant frequency for the transducer and generator. Even when the generator is tuned to the resonant frequency of the transducer during initial set-up, changes occur which change the resonant frequency of the transducer during actual operation. It is common practice to build a wire bonder or die bonder and to set up the resonant frequency of the transducer and generator without applying actual load conditions which effect the resonant frequency of the transducer. It is known that the changes in the resonant frequency of the transducer also affect the phase of the phase lock loop which cause the phase between current and voltage to change in a direction which is other than zero.
Heretofore, it was necessary to manually set-up the wire or die bonder power supply generator and to allow the bonding machine to warm up and stabilize. Then the transducer could be loaded under actual or simulated conditions to permit manual setting of the frequency of the generator to the resonant frequency of the transducer under load, however, the resonant frequency of the transducer changes under actual manufacturing conditions. In these prior art systems, it was also necessary to use special instrumentation and make time consuming manual set-up adjustments every time there was a tool or device type change on a bonding machine which occurs as often as every shift. Many manufacturers employing automatic wire and die bonders would not take the necessary time to make the proper adjustments and the quality of the semiconductor devices being manufactured has suffered as a result.
Prior art power supply generator systems may be characterized as set it and forget it. Prior art power supply generator systems depended on having a highly accurate transducer whose resonant frequency was known and made to a tight specification. Prior art transducer and power supply systems did not incorporate means for transmitting optimum power to the transducer system. Prior art power supply generator systems were made to such a tight specification that it was possible for the phase lock loop to be incapable of tracking the resonant frequency of the transducer. Prior art power supply generators did not monitor the condition of the ultrasonic system and as a result of this and the other aforementioned problems did not produce consistent bond quality. When the power supply generator system properly monitors the ultrasonic system, the information available may be employed to monitor both bond quality and to determine missing wires.
It would be desirable to eliminate the time consuming manual set-up and preparation necessary to prepare a wire or die bonder for production operations. Further, it would be desirable to provide a system which automatically tunes the ultrasonic power supply generator to the resonant frequency of the loaded transducer under actual bonding conditions in a few seconds and continues to track and lock onto the resonant frequency of the loaded transducer under operating conditions.